Pasty multi-component masses, such as dental impression masses, are prepared by mixing devices in which the individual components of the mass are simultaneously supplied from separate cartridge cylinders to a mixer which dispenses the mixed paste from a front end. The mixer may be a static mixer or a dynamic mixer (having a rotary mixer element). The paste exiting from the front end of the mixer may be supplied directly onto an impression spoon or tray.
Examples of dynamic mixers are found in, e.g., WO 00/21652, EP-A-1 149 627, U.S. Pat. No. 5,249,862 or DE-U-297 05 741. These known dynamic mixers have as their rear end (inlet side) a central hexagonal opening for coupling to a drive shaft for rotating the inner body of the mixer, and further two additional inlet connectors for feeding the components which are to be mixed.
Depending on the viscosity and mixing ratio, the fact that the pressure builds up differently in the individual cartridge cylinders at the start of the device may cause the components to reach the mixer at different times. In such a case, the initial volume of paste exiting from the mixer has a mixing ratio which differs from a desired value and may therefore cure less perfectly or more slowly, or have other undesired properties.
U.S. Pat. No. 6,244,740 suggests a mixer for producing multi-component pastes. This dynamic mixer contains a deviating channel provided between the inlet opening for the component of the larger volume proportion and the mixing chamber, in order to delay the feed of this component with respect to the other component. Typically, the flow of the base paste is thus delayed compared to the flow of the catalyst.
US-A-2004/085854 describes a dynamic mixer having a delay chamber provided between the inlet opening for the component of the larger volume proportion and the mixing chamber, in order to delay the feed of this component with respect to the other component. The delay chamber has, inter alia, a boundary wall located in the flow direction of a paste component, on which the paste component backs up. The delay chamber also has at least one opening, which opens into the mixing chamber and which is arranged to be set back with respect to the boundary wall. The term set back in the sense of this invention is to be understood to mean an arrangement in which the opening does not adjoin the boundary wall directly but is arranged offset from the latter (see paragraphs [0040] and [0041]). The component flows into the mixing chamber only after the delay chamber is filled.
Mixers having channels of different lengths between the inlet openings of the mixer and the mixing chamber are described, e.g., in DE-U-203 02 987, U.S. Pat. No. 6,523,992, and US-A-2003/123323.
Further improvements in the mixing and dispensation of a mixed paste having a desired ratio of first and second components would be desirable.